Originally Posted by
Commodus
That's just a fancy way of saying, "if you scrape the film from an area, it will re-oxidize."
Rust is also 'self healing'. If you scrape the rust off a steel tube, it will re-rust.
yes, the difference is that rust will continue to pit into the material, but with Ti and Al, the oxidation layer seals off the inner material and prevents further oxidation from continuing.